1. Field of the Invention
The present invention relates to a multi charged particle beam writing apparatus and a multi charged particle beam writing method. More specifically, the present invention relates to a multi beam writing apparatus and method capable of correcting a positional deviation due to the amount of charge (electrification) when a pattern is written onto a target object using multi electron beams, for example.
2. Description of Related Art
The lithography technique that advances miniaturization of semiconductor devices is extremely important as a unique process whereby patterns are formed in semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. The electron beam (EB) writing technique, which intrinsically has excellent resolution, is used for writing or “drawing” a pattern on a wafer and the like with electron beams.
As an example employing the electron beam writing technique, a writing apparatus using multiple beams (multi-beams) can be cited. Compared with the case of writing a pattern by using a single electron beam, since it is possible to emit multiple beams at a time in multiple writing, the throughput can be greatly increased. For example, in the writing apparatus employing a multi-beam system, multiple beams are formed by letting an electron beam emitted from an electron gun assembly pass through a mask with a plurality of holes, blanking control is performed for each of the beams, and each unblocked beam is reduced by an optical system and deflected by a deflector so as to irradiate a desired position on a target object or “sample”.
When a target object, such as a mask, to which a resist film has been applied, is irradiated with multiple beams, the irradiated position and its periphery may have been charged with multiple beams previously irradiated. The positional deviation due to this charging phenomenon has not been conventionally regarded as a problem in the multi beam writing apparatus. However, with the pattern miniaturization as described above, such positional deviation due to the charging phenomenon has become a problem. In particular, improvement of the pattern position accuracy of photomasks is required more than ever because a double patterning technique has been introduced.
Conventionally, as a method for correcting a positional deviation of a position irradiated by the beams, with respect to a single beam writing system, there has been known to form a charge dissipation layer (CDL) on a resist layer in order to prevent charging of the resist surface. However, since the charge dissipation layer basically has acidic properties, it has a poor affinity for a chemically amplified resist. Further, there is a need to provide new equipment in order to form the charge dissipation layer, thereby increasing the manufacturing cost of a photomask. For this reason, it is desired to perform charging effect correction (CEC) without using the charge dissipation layer.
With regard to a positional deviation correction amount caused by charging, as to a single beam writing system, there is proposed a writing apparatus which calculates a correction amount of positional deviation of a beam irradiation position, based on an electric field strength, and applies a beam based on the correction amount (refer to, e.g., Japanese Patent Application Laid-open (JP-A) No. 2007-324175). According to such a writing apparatus, a positional deviation amount distribution is calculated from an irradiation amount distribution through a linear response function assuming that there exists a linearly proportional relationship between the irradiation amount distribution and a charge amount distribution.
With respect to a multi beam writing system, since irradiation is simultaneously performed with multiple beams at a time, it needs to consider the influence from the surrounding beam. Thereby, it is assumed that a further device different from that of a single beam system is required. However, with respect to a multi beam writing system, a method for exactly correcting a positional deviation of the irradiation position due to the electrification phenomenon has not been conventionally established.